This invention relates to anionic alkoxylate surfactants and to their use in preparing aqueous polymeric dispersions.
Nonionic alkoxylate surfactants have been known for many years and they have been used in many industrial applications including the preparation of aqueous polymeric dispersions. These non-ionic alkoxylate surfactants typically consist of a hydrophobic portion or chain which is covalently bonded to a poly(oxyalkylene) chain, especially poly(oxyethylene), which provides the hydrophilic portion of the surfactant.
WO91/13849, the entire contents of which is incorporated by reference, discloses fatty alcohol alkoxylate surfactants in which the fatty alcohol chains contain a pair of conjugated double bonds having opposite geometric isomerism which are reactive in dispersion polymerisation. These surfactants are described as being useful as stabilisers in the preparation of aqueous dispersions of film forming addition polymers.
In certain aqueous dispersions of polymerisation preparations the solely nonionic characteristics of these stabilisers means that relatively high levels of stabilisers are required to be used to prepare the desired fine particle size aqueous dispersions. This may add to the raw material costs of such dispersions and/or cause a degradation in resulting film properties, especially properties associated with high levels of water soluble species such as early water resistance. The solely nonionic character may also result in limitations in processing conditions. For example, with this class of surfactants lower temperature polymerisation is often required to provide dispersions with low levels of coagulum. These lower temperatures may result in extended processing time and hence increased manufacturing costs.
The use of small amounts of anionic surfactants in combination with these prior-art non-ionic stabilisers is capable of producing the desired small particle size dispersions while maintaining the desired low levels of non-ionic stabiliser. However, these polymer dispersions suffer from problems commonly associated with the use of conventional anionic surfactants. These include residual water sensitivity in films formed from such aqueous dispersions, intolerance to polyvalent species and foaming.
The alkylphenol hydrophobe has exceptional adsorption onto hydrophobic surfaces and therefore generally has superior performance to aliphatic analogues. Alkylphenol ethoxylate non-ionic surfactants have been previously converted to anionic sulfates or phosphates and this class of surfactant has been known for several years. However, this class of anionic alkoxylates can also lead to residual water sensitivity in films formed from aqueous film forming dispersions prepared with this class of surfactants as stabilisers. Additionally, alkylphenol ethoxylates are thought to be environmentally unfavourble due to their poor biodegradability and subsequent aquatic toxicity.
Anionic alkoxylate surfactants are claimed in U.S. Pat. No. 4,939,283 by Yokota et al. These surfactants are typically prepared by reacting a hydrophobe such as nonylphenol (1 mole) with allyl glycidyl ether (1 mole) and condensing ethylene oxide (10-50 moles). The terminal hydroxyl is then converted to the sulphate ester, phosphate ester, sulfosuccinate half ester or sulfosuccinate diester. Salts of these species are included and these are the alkali metal, ammonium and low alkanolamine salts. These surfactants offer some improvement in colloidal stability. However, in certain applications they appear to be less useful and it is speculated that this may attribute to the relatively low reactivity of the meth(allyl) unsaturated group in certain copolymerisation reactions.
It is an object of the present invention to overcome or at least alleviated one or more of the problems associated with the stabilisers described in the prior art.
Accordingly the present invention provides an anionic alkoxylate surfactant of the formula I 
where R is a di- or tri-unsaturated C4-22 straight or branched hydrocarbon chain, at least two double bonds of said unsaturated chain being conjugated and exhibiting opposite geometric isomerism;
m is 0 or 1;
Y is O or NRxe2x80x2;
each Rxe2x80x2 is independently selected from hydrogen, C1-6 alkyl and phenyl; n is 1 to 50; and OX is a anionic group selected from the group consisting of acids or salts of sulphate, phosphate, sulphosuccinate, succinate, carboxymethyl, maleate, carboxyethyl, alkenylsuccinate, phthalate, sulphoethyl, 3-sulpho-2-hydroxypropyl, sulphopropyl, oxalate and citrate.
Preferably the surfactant has an R group of the following structure:
CH3xe2x80x94(CH2)13-Kxe2x80x94CH=CHxe2x80x94CH=CHxe2x80x94(CH2)Kxe2x80x94
where K is 8 or 9.
Preferably R is a surfactant accordingly to claim 1 wherein R is derived from linoleyl or linolenyl alcohol or acid by alkoxylation of said alcohol or acid.
The 
units may be the same or different.
Preferably at least one Rxe2x80x2 on the or each xe2x80x94(CHRxe2x80x2xe2x80x94CHRxe2x80x2xe2x80x94O)xe2x80x94 unit is hydrogen. More preferably both Rxe2x80x2 on the or each xe2x80x94(CHRxe2x80x2xe2x80x94CHRxe2x80x2xe2x80x94O)xe2x80x94 unit are hydrogen.
Preferably OX is sulphate, phosphate, sulphosuccinate, carboxymethyl or a salt thereof.
Preferably the salt is an amine, ammonium or alkali metal salt.
The surfactant of formula I is preferably derived from a fatty alcohol such that m is 0. The surfactant may also be derived from fatty acid esters, fatty amines, and fatty acid amides. Where Y is NRxe2x80x2, Rxe2x80x2 is preferably H or CH3.
The invention provides in an alternative form an aqueous dispersion of polymeric particles wherein the dispersion is formed in the presence of a stabilising amount of anionic alkoxylate surfactants as described above.
Preferably the polymer dispersion is prepared by addition polymerisation of addition polymerisable monomer. Preferably the addition polymerisable monomer is an ethylenically unsaturated monomer.
Preferably the polymer dispersion is film forming at or near ambient temperature with the optional use of external plasticisers.
The aqueous dispersion may also be prepared by dispersion of a condensation polymer.
The invention also provides the use of an anionic surfactant as described above as a stabiliser in the preparation of an aqueous dispersion of polymeric particles, or as a substitute for alkylphenol based surfactants in the preparation of aqueous dispersion of polymeric particles and coating compositions.
The anionic alkoxylate surfactants of the present invention can be prepared by first forming alkoxylate product on a suitable hydrocarbon chain and then converting the hydroxyl group to an appropriate anionic species. Preferred hydrocarbon chains are the fatty chains of unsaturated fatty alcohols. The preferred alkylene oxides are ethylene oxide.
As well, as for example, condensing fatty alcohol with ethylene oxide, other alkylene oxides can be used either alone or as a mixture. For example, a random co-polymer of ethylene and propylene oxide can be used. Alternatively a block alkoxylate copolymer could be prepared by first reacting a fatty alcohol with, for example, propylene or butylene oxide and then condensing this adduct with ethylene oxide. Similar alkoxylation products can be obtained from the corresponding esters, amines and amides.
The fatty alcohols that are preferred are the C18 fatty alcohols, linoleyl and linolenyl alcohols. Other fatty alcohols and or the corresponding fatty acids can be used. In certain embodiments fatty amines and fatty amides may be used as the hydrophobe of the surfactants. Fatty alcohols of other chain lengths may be used, the most preferred having 10-22 carbon atoms. The corresponding carboxylic acids, etc. are also suitable.
The poly(oxyalkylene) chain length of the surfactant corresponds to that from 1-50 alkylene oxide units. The nature of the individual units is very much determined by the end use to which the compound will be put. For example, if the compound is to be a reactive surfactant in an aqueous emulsion polymerisation system, the poly(oxyalkylene) chain will consist mainly, and preferably solely, of poly(oxyethylene) units. Provided that the desired balance between the lipophilic and hydrophilic portions of the surfactant can be achieved, it is possible to include a proportion of oxypropylene, oxybutylene or oxyphenylethylene units. These are advantageously located on the chain adjacent to the lipophilic portion as they increase the overall lipophilcity of the molecule. However they may be arranged in the opposite fashion. It is important to note that the overall character of the surfactant is determined after the anionic species is introduced. Compared with wholly non-ionic surfactants generally shorter hydrophilic chains are possible as well as slightly less hydrophilic poly(oxyalkylene) chains. The preferred poly(oxyalkylene) unit is the poly(oxyethylene) unit and preferably all of the poly(oxyalkylene) units are poly)oxyethylene) units.
The compounds of this invention may be synthesised by any convenient means. A particularly useful method of preparing the precursors to the preferred compounds is the reaction of alkylene oxide with a fatty alcohol in the presence of a base catalyst which is a Bronsted base.
It will be readily appreciated that in the case of linoleyl alcohol the structure of this alcohol is different to that of the non-oxyalkylene chain part of the surfactant compounds; linoleyl alcohol is cis-9, cis-12-octadecadienol. As described in WO91/13849, under alkoxylation conditions, one of the double bonds positioned at the 9- or the 12-position transfers into a conjugated arrangement with respect to the other, and at the same time this bond changes its stereochemical configuration such that there is one cis-bond and one trans-bond.
The linoleyl alcohol for use in this preferred aspect of the invention maybe a pure substance. Alternatively, it is possible to use one of the commercially-available mixtures of fatty alcohols which contain a significant proportion of linoleyl alcohol. It has been found that the alkoxylation of such mixtures can give a product which is acceptable for many uses and which is considerably cheaper than using pure linoleyl alcohol. Examples of suitable commercially-available mixtures can be found in the xe2x80x9cOcenolxe2x80x9d range of product of Henkel KGaA, one suitable one being the xe2x80x9c110-130xe2x80x9d grade.
By xe2x80x9cBronsted basexe2x80x9d is meant a base which is capable of abstracting a proton. While any Bronsted base will work to some extent in the invention it will readily be appreciated by the skilled worker that, for some bases, the obtaining of acceptable yields will require unacceptably long reaction times and/or unacceptably severe reaction conditions, and the use of such bases is not therefore a practical proposition. As a general rule, reaction times should be no longer than 48 hours and reaction conditions no more severe than 160xc2x0 C. temperature and 1000 kPa pressure. Any Bronsted base which gives an acceptable yield under conditions such as these is especially preferred for use in this invention. Examples of preferred bases are the alkali metal and alkaline earth metal alkoxides and hydroxides, particularly sodium methoxide and potassium hydroxide. Other suitable bases include metal hydrides, such as sodium hydride.
The anionic species may be introduced into the surfactant precursor in a number of ways. It is important that the method selected does not cause the unsaturation in the hydrophobe to be altered or such that it no longer remains within the scope of Formula I. Examples of suitable methods are as follows:
Phosphate ester derivatives can be made by reaction of the alkoxylate species with either phosphorous pentoxide or polyphosphoric acid. The former result in a mixture of mono- and di-alkyl phosphate derivatives whereas the latter gives primarily the monoalkyl derivative; the corresponding salts can be prepared from the acid form of the phosphate by neutralisation with, for example, alkali metal hydroxides or ammonia.
Sulphate esters are preferably made with sulfamic acid as the sulfating reagent: the ammonium salt of the sulphate will be initially formed and this can be converted into an alkali metal salt, if required, by reaction with an alkali metal hydroxide, with release of ammonia: sulphur trioxide is an alternative sulfating reagent but this may result in reaction with the double bond system of the hydrophobe and is not preferred. Carboxymethyl derivatives of the alkoxylate species can be made by reaction with sodium chloracetate in the presence of base. Succinates, maleates, phthalates and alkenylsuccinates can be prepared by reaction of the alkoxylate with the corresponding anhydride: neutralisation of this condensate with alkali metal hydroxides or ammonia provides the corresponding salts. Further reaction of the maleate with sodium bisulphite leads to the sulphosuccinate derivatives. The methods of U.S. Pat. No. 4,939,283 are also incorporated by reference.
Aqueous polymeric dispersions using the surfactants of the present invention can be prepared by addition polymerisation of ethylenically unsaturated monomers. Alternatively the polymer dispersion may be a condensation polymer such as an alkyd resin prepared from drying to semi-drying vegetable oil. In the case of an alkyd resin a hot melt mixture of the surfactant and alkyd resin can be prepared and emulsification in water can be carried out by addition to water under mechanical agitation. Phase inversion techniques are also able to be used whereby water is added under agitation to the melt until phase inversion takes place. In addition ultrasonic and other known methods of emulsification can be used. It is believed that the unsaturated groups on the hydrophobic portion of the surfactants of the present invention participate in autoxidation reactions with other surfactant molecules and/or the alkyd resin to give film properties with improved hardness. This is believed to occur because the surfactant covalently bonds to the polymeric dispersion.
As stated above the polymer dispersion may be prepared from addition polymerisable ethylenically unsaturated monomers.
The nature of the unsaturated monomer is not narrowly critical and particles may be prepared by this process using a wide range of monomers commonly used in suspension and emulsion polymerisation, for example, one or more of the monomers selected from the group of the C1-12 (preferably the C1-4) alkyl acrylates and methacrylates, (meth)acrylates and methacrylates, butyl methacrylate, stearyl methacrylate, methacrylic acid, methoxypropyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, dimethylaminoethyl methacrylate, N-butoxymethyl methacrylamide, N-butoxymethyl acrylamide, glycidyl methacrylate, vinyl acetate, vinyl propionate, styrene and vinyl styrene, vinyl toluene, methoxy styrene and vinyl pyridine, di-butyl maleate and vinyl chloride.
The known techniques of suspension and emulsion polymerisation, including the selection of appropriate polymerisation initiators, are applicable to the preparation of the aqueous dispersions of this invention. As is understood in the art polar monomers may need to be used in combination with less polar monomers to achieve suitable aqueous polymeric dispersions. Either thermally activated or redox initiators may be used.
Due to the reactivity of the compounds of Formula I they have been found to provide a particularly stable dispersion of polymer particles therefore providing a significant improvement in aqueous coating compositions.
The aqueous dispersion may comprise additives which adapt it for use as a coating composition.
Coating compositions may be prepared by blending standard additives such as pigments, extenders, antifoams, thickeners and fungicides into the dispersion in art-recognised quantities using known methods.
An example of polymer particles which may be produced using the compounds of Formula I is described in U.S. Pat. No. 4,413,073.
A further preferred example of polymer particles which may be prepared using compounds of Formula I are core-sheath particles of the type described in Australian Patent Application No. 52006/90. Such particles will have diameters of less than 100 nm and comprise a core of polymer of an ethylenically unsaturated monomer and a sheath comprising poly(oxyalkyene) chains are derived from the covalent bonding of compounds of Formula I with the core addition-polymer.
The invention will be further described by reference to the following non-limiting examples in which all parts are expressed by weight.